Centrifugal casting apparatus with smooth refractory nonhydrocarbon mold coating



M. N. ORNITZ 3,437,131

APPARATUS WITH SM H REFRACTORY DROCARBON MOLD COAT April 8, 1969CENTHIFUGAL CAS I 6 Sheet Filed 001:. 7, 1965 INVENTOR Martin N. OrnitzApril 8, 1969 Filed Oct 7 1960 INVENTOR 3,437,131 EFRACTORY Sheet Z M.N. ORNITZ APPARATUS WITH SMOOTH R NONHYDROCARBON MOLD COATINGCENTRIFUGAL CASTING United States Patent US. Cl. 164-298 7 ClaimsABSTRACT OF THE DISCLOSURE A centrifugal casting mold is provided withan annular stop member receiving recess at each end, means for rotationof the mold and a smooth refractory coating adhered to the mold surfacesbetween said recesses to provide a thermal barrier for elimination ofchills in metal cast therein.

The present invention relates to the manufacture of tubular metalcastings and is directed particularly to certain improvements in themanufacture of such castings by centrifugal techniques in permanentmetal molds. The molds may be rotated horizontally or substantially soabout their longitudinal axes.

When employing centrifugal casting techniques in this manner andparticularly when casting a relatively long tubular member, the art haslong been confronted with the problem of producing a casting in whichthe metal is completely fused throughout the length of the casting andwhich has a smooth, substantially defect-free outer surface. Inparticularly, it has been difficult to obtain a centrifugal casting inthis manner, especially in the greater lengths and diameters thereof,which has an acceptable surface smoothness without further finishing.

These problems are more or less acute depending upon the particularmethod of centrifugal casting employed, and in any case an acceptablesolution thereto has not hitherto been found.

During conventional centrifugal casting operations, it has been foundthat when the advancing molten metal slips over the rotated mold, movinglengthwise thereof intermittently and/ or too rapidly, it tends toresult in the formation of pin holes originating in the outer surface ofthe casting. Laps or cold shuts are produced when the leading edge ofthe molten metal moves longitudinally of the mold more or lessintermittently and/or discontinuously, at a speed such that it becomesso thin that it rapidly cools, prematurely solidifies and also oxidizes,to such an extent that it does not properly weld to or unite with themass of metal which subsequently flows over it as the distribution ofthe charge progresses. These pin holes, laps or cold shuts sometimesextend throughout the thickness of the wall of the casting, but usuallyoccur only in the outer portion of the wall, i.e., in the outer surfaceof the casting.

In one particular method of centrifugal casting heretofore employed, theproduction of cast tubular members in centrifugal molds involves thepouring of the charge of molten metal into the metal mold in such amanner that the distribution of the metal longitudinally of the mold iseffected primarily by the action of centrifugal force. A common way ofdoing this is to pour the metal from a spout occupying a relativelyfixed position lengthwise of the mold and located, for example, at oneend thereof. However, attempts to produce long tubular castingscentrifugally by such method have heretofore resulted in the formationof castings having the aforementioned pin holes and laps or cold shutswhich render the castings commercially unacceptable.

3,437,131 Patented Apr. 8, 1969 ICE In another centrifugal techniquewhich is widely employed commercially, the molten metal is delivered tothe mold by means of a pouring trough relatively retractable over thelength of the mold so that molten metal is deposited progressively toform a helix, the convolutions of which fuse together to form anintegral structure. In this method, the metal is distributedlongitudinally of the mold surface primarily by means of the retractivepour, and the centrifugal force holds the molten metal against the mold,as an all centrifugal casting. However, in actual practice, the metalupon being so deposited does spread to some extent because of thelateral pressure resulting from the centrifugal force, and is thuscaused to flow longitudinally of the mold to advance beyond the helicalzone of metal deposition. This spreading is sometimes excessive, and isfrequently irregular, or, as it is sometimes called, discontinuous onthe leading edge, and thus also results in the formation of excessivelythin olfshoots which solidify almost instantaneously and, therefore,produces the aforementioned laps or cold shuts in at least the outersurface portion of the casting. While this method reduces thetroublesome defects, it does not solve the problems to which referenceis made above.

In connection with more recently developed centrifugal techniques of theprior art, it has been conjectured that the aforementioned pin holes andother defects have resulted from a too rapid advance of the molten metalin moving lengthwise of the mold without suf'ficiently partaking of therotational motion of the centrifugal mold. Thus, it was proposed toprovide the mold surfaces with a coating having a large number ofprotuberances, which would hasten the molten metal pick-up by thecentrifugal mold and at the same time would slow the lateral advance ofthe molten metal throughout the mold. This method was successful to someextent in reducing the pin holes and laps or cold shuts referred topreviously, but it had the effect of limiting the length of the tubularcasting to the order of about 3 or 4 times its outside diameter. Formost applications, moreover, the surface of the centrifugal casting wascommercially unacceptable due to the rough outer surfaces thereofproduced by the intentionally roughened mold surfaces.

In a more recently developed method, a resin-bonded sand is coated uponthe mold surface for the purpose of slowing down the cooling rate in theproduction of cast iron piping by centrifugal techniques. The lateraladvance of the molten metal throughout the centrifugal mold also isslowed down in this method due to the roughness of the sand coating.Although this method involves some improvement over prior methods, theresultant surfaces of the casting still are not sufficiently smooth formany commercial applications. The restricted lateral movement of themolten metal, by the resin-bonded sand coating, also limits the lengthsof centrifugal castings which can be fabricated by this technique.

The centrifugal casting technique disclosed herein overcomes theseproblems by providing a centrifugal mold which permits rapid lateraltransfer of the molten metal to the extremities thereof before themolten metal has an opportunity to develop localized congealing and theforementioned pin holes and laps or cold shuts. The outer surface of thecasting, moreover, is free from defects, is smooth, and does not requirefurther finishing. These aims are accomplished by the presentcentrifugal casting technique which provides a centrifugal mold havingan exceptionally smooth refractory coating upon the mold surfacesthereof to promote rapid lateral advance of the molten metal and toprovide an exceptionally smooth outer surface of the finished casting.The mold coating desirably is formed from suitable refractory materialswhich will not decompose at elevated temperatures with attendantoxidation of adjacent molten metal. The refractory coating also isapplied in sufficient thickness, in accordance with another feature ofthe centrifugal casting technique, to provide a uniform thermalinsulation for the molten metal throughout the length of the centrifugalmold to prevent localized congealing or chills in the molten metal. Thedisclosed centrifugal casting technique also contemplates a novel methodfor the application of such coating to the centrifugal mold. Thiscoating method, for many applications results in a coated mold Which canbe used directly due to the smoothness of the coating. Where anextremely smooth surface finish of the casting is desired, the coatingmethod of the disclosed casting technique produces a sufficientlyadherent mold coating which can be further smoothed, prior to use of themold, by conventional techniques, such as sanding.

The apparatus of the present invention makes possible the production oftubular castings made of steel or other metals or alloys, of a lengthnot hitherto possible without exhibiting the aforementioned pin holesand laps or cold shuts, as would detract from the quality of thecastings or render them commercially unacceptable. The centrifugalcastings thus produced meet presentday standards of surface finisheswithout further grinding, polishing, or other smoothing operation.

The apparatus disclosed herein facilitates centrifugal castingtechniques by promoting the distribution in both the circumferential andlongitudinal directions of the molten metal poured into the mold. Therate of pick-up of the molten metal by the mold can be accelerated by amore rapid rotation of the mold. At the same time, the longitudinaldistribution of the molten metal is accelerated by the provision of avery smooth mold coating, the thickness and character of which providesa thermal barrier for the molten metal. The heat flow to the mold fromthe leading edge of the longitudinally advancing molten metal issufiiciently arrested to maintain the leading edge at a temperature tofuse the leading edge portion with molten metal which subsequently flowsthereover.

This is accomplished by controlling the thickness of the mold coating inrelation to the outside diameter of the centrifugal casting to providethe required thermal insulation depending upon the amount and thicknessof the molten metal being cast. The mold coating is provided withuniform smoothness which, in accordance with the disclosed coatingtechnique, in turn produces uniformity of coating thickness throughoutthe length of the mold to prevent the development of chills or coldspots as the molten metal flows longitudinally of the mold. At the sametime, the acceleration in rate of longitudinal metal fiow provides animmediate fusion of the leading edges of metal flow with subsequentflows to ensure complete fusion therebetween.

The aforementioned mold coating can be applied, for example, by sprayinga liquid suspension of the coating material on the mold, and theaforementioned required properties of the coating can be varied andcontrolled by proper selection of spraying equipment in accordance withthe invention and by regulation of the spraying operation.

A composition which has been found suitable for providing a coatinghaving the desired characteristics referred to above is composed of asuspension of zircon flour, diatomaceous earth, and bentonite in water,and is applied to the mold by a spraying operation in which thecomposition is atomized and discharged on the inner surface of the metalmold by a relative reciprocation of a spray nozzle thereover, while themold is rotated. The speed of rotation of the mold during the sprayoperation is found to be critical for optimum coating characteristics,including smoothness, and the desired or optimum speed of mold rotationis found to vary with the size of the mold.

While the coating composition can be varied, a uniform aqueoussuspension made up of 87% by weight of zircon flour, diatomaceous earth,and 3% bentonite, with enough water to mix to a 60 Baum, has proven tobe satisfactory for many applications, The particles of zircon flourshould be of such fineness that the composition is sprayable in anatomizing type of spray equipment, and are desirably of about #325 seivesize or finer. The bentonite aids in keeping the ziron flour insuspension While the diatomaceous earth increases the thermal impedanceof the coating. It will be realized that other equivalent coatingexpensions can be utilized in keeping with the aims of the invention,for example, one or more of the coating compositions disclosed andclaimed in applicauts copending and coassigned application entitled MoldCoating Composition Particularly for Centrifugal Molds, filedconcurrently herewith, Ser. No. 493,917.

In the application of one of the aforementioned compositions to theinner surfaces of the mold, it is essential that the composition beatomized and sprayed on the mold at such a rate that the water or othercarrier liquid will undergo a controlled evaporation so that the sprayedglobules will contact the mold surface and merge with one another toproduce a very smooth and adherent coating. In furtherance of thispurpose, the spray nozzle is held as close to the mold surface aspossible without causing the coating to run and a maximum condition ofatomization is utilized. During the coating process the mold is rotated,which improves the resulting smoothness of the coating. For a mold ofrelatively small diameter, for example about 9 inches, the speed ofrotation is about 800 rpm. while for larger mold diameters the speed ofrotation is correspondingly slower. As an example, a rather larger moldof about 17 inches in diameter, requires a rotational speed of about 500rpm.

The rotational speed is varied with variations in the lance speeds.Excessive rotational speed detracts from longitudinal distribution ofthe coating and should be avoided. Coating may be applied attemperatures as high as about 700 F., considerably above the temperatureof conventional coatings.

The quality of the coating surface can be readily varied from a fairlysmooth as-sprayed condition, to a very smooth surface condition bysanding or grinding or other surface treatment depending upon theapplication of the invention or surface finish requirements of thecentrifugal casting. For very long castings, such surface treatment isdesirable to further accelerate the longitudinal flow of the metal moldthroughout the centrifugal mold.

While different forms of nozzles or spray heads can be utilized inapplying the coating composition, it has been found most beneficial tosupport the spray nozzle such that the major proportion of the sprayissuing therefrom is directed normally of the mold surface, i.e.,substantially at right angles to the longitudinal axis of the mold. Forcertain sizes of molds it has been found best to employ a fan type spraynozzle while for other sizes, for example, the smaller sizes, aring-type spray is found to be more effective. In either case, the sprayis directed substantially normally of the mold surface as aforesaid.

As an example, the smaller sizes of centrifugal molds in the order of 9inches in diameter or under are coated with a ring-spray nozzle which isreciprocated longitudinally within the bore of the mold and desirablyconcentrically therewith. For the type of spray equipment notedhereinafter, and mounted on a suitable lance or other support, thesmaller sizes of centrifugal molds can be rotated at a stationarylocation and the spray nozzle support or lance can be fed axiallytherethrough at a rate of about 27 feet per minute while the mold isbeing rotated at the aforementioned speed.

In the case of the larger sizes of molds, i.e., over 9 inches indiameter, the fan-type nozzle can be similarly mounted, with theexception that the lance or support may be mounted eccentrically of themold axis depending upon the size thereof, in order to hold the spraynozzle at the proper distance from the mold wall. In the latterarrangement, a fan spray nozzle is preferred and is supported such thatthe axis of the spray fan is substantially normal to the axis of themold and to the mold surface. In one example, the lance feed of the fannozzle is at the same rate for the larger mold sizes or about 27 feetper minute while the rotational speed of the mold is correspondinglyless, being about 500 r.p.m. for the 17 inch diameter mold noted above.

The proper rotational speed of the centrifugal mold during the sprayoperation permits the spray nozzle to be located rather close to themold surfaces without danger of the coating running, owing to thecentrifugal forces developed. A smoother and more adherent coating isthereby obtained. If the rotation of the mold is too slow, theaforementioned coating runs will be encountered; on the other hand ifthe rotational speed is too high, accretional build-up in the coatingwill occur producing roughness owing to the premature evaporation of thecoating carrier liquid and to lag in rotational pick-up of the coatingby the rotating mold. Increasing the distance of the nozzle from themold surface will also tend to increase the roughness of the coatingsurface as a result of excessive evaporation. Increasing the density ofthe coating suspension will also aid in preventing coating runs as longas the density is not increased to the extent to interfere with properatomization of the coating when sprayed. On the other hand, a decreasein coating density can render the coating difficult to maintain inproper suspension during the coating application.

The thickness of the applied coating can be varied optimally with thesize of the centrifugal and the quantity of molten metal to be depositedtherein. The coating thickness for a given nozzle is selected such thatan adequate thermal barrier is provided to prevent premature cooling ofthe molten metal as it flows longitudinally along the mold. It has beenfound that the average thickness of a coating of one of theaforementioned compositions can vary within a range of from 0.005 inchto .08 inch for the smaller sizes of molds of about 9 inches and underand between .08 inch and 0.125 inch for the larger mold sizes. Withineach range of mold sizes the thickness of the coating can be varied tosome extent With casting conditions, such as with the particularcentrifugal casting method employed, the metal being cast, and thelength and diameter ratio of the tubular casting, the Wall thickness ofthe casting, and the particular coating composition used. For example, athinner mold coating can be utilized by increasing the proportion ofdiatomaceous earth in the coating composition in order to ensure anadequately high thermal impedance.

The aforedescribed coating method produces a mold coating which adherestogether and to the mold and yet which is suffiicently friable upon thecompletion of the casting operation that the coating facilitates theready withdrawal of the casting from the mold. This coating appears tobe somewhat more friable following the casting operation than before it,but will adequately resist the washing away effect of the molten metalstream as it is poured into the mold. It may also be noted that thefria-bility of the coating can be varied and controlled by varying theproportion of the bentonite in the coating suspension.

A mold coating for the aforedescribed purposes is of a temporarycharacter, and is applied to the mold before each casting operation.After the application of the coating, the coated mold may be subjectedto handling, inspection, recoating and/or storage as required withoutinterfering with its subsequent use. Upon the withdrawal of the casting,the coating may, because of its friability, be readily removed orstripped from the mold by means of a wire brush, jet of compressed air,or the like to facilitate preparation of the metal mold for the nextcasting. As the same mold is used repeatedly its temperature rises fromthe heat given off by the metal being cast. It is the the practice tocool the mold with water sprays to a temperature snfiiciently low toaccept the mold coating. The

present coating may be applied at higher temperatures up to about 700F., thereby requiring less coolant and less lost time in preparation.

Various other compositions can be used in the practice of the inventionto provide, when sprayed upon the mold, a refractory coating having therequisite thickness and surface smoothness to provide the thermalbarrier action, to facilitate longitudinal movement of the metal mold,and to afford a smooth outer surface of the casting. For instance, whilezircon flour is a most satisfactory refractory, and when applied in theabove described suspensions, produces the necessary thermal impedance,other suitable refractory materials, for example, the oxides ofaluminum, magnesium, beryllium, silicon, chromium, titanium, or mixturesor compounds thereof alone or with other compounds such as mixtures offorsterite and fayalite, can be utilized depending upon the applicationof the invention, the metal being cast, etc. The use of zirconia isdesirable for many applications, however, because of its nontoxicity,its smooth surface characteristic as sprayed, and its higher fusiontemperature permitting the molten metal to be poured at a hottertemperature. As indicated above, bentonite has been found to be asatisfactory binder as it serves not only as a binding agent for therefractory particles but also as a suspending agent for the coatingparticles in the liquid carrier. Nevertheless, other suitable bindingagents can be utilized, provided they have the necessary adhesivequalities to enable the coating to withstand the forces exerted thereonby the charge of molten metal, as Well as to adhere properly to themetallic mold surfaces, and are sufiiciently refractory and free ofcomponents tending to emit gases during the casting operation. The useof diatomaceous earth increases the thermal impedance of the refractorymaterial and serves also as an inert binder for the coating suspension.On the other hand, this latter component increases the friability of thecoating particularly following the casting operation and thus permitseasy stripping of the casting from the mold in preparation forsucceeding casting operations. Other suitable and known materials can beutilized for these purposes providing that they exhibit the necessaryadhesive and thermal properties. For example, additional bonding actioncan be imparted to the coating through the addition of relatively smallamounts of sodium silicate in the range of about 0.25 to 4%, and isparticularly useful under those conditions where the mold coating tendsto spall. Furthermore, while water is a convenient carrier vehicle forthe solid ingredients of the composition, it is to be understood thatany other suitable liquid can be employed for this purpose. While acoating density of about 60 Baum is desirable for most applications ofthe invention, it is contemplated that sufiicient carrier liquid can beutilized to obtain a range of coating densities from about 50 to Baum.If the coating suspension is too fluid, such as under 50 Baum, it willsettle to rapidly and requires continuous agitation during the sprayingoperation; on the other hand, if the Baum density is too high, thesuspension becomes too thick for optimum spraying conditions. Regardlessof the particular composition used in the practice of the invention, itis to be noted that the thickness and attendant thermal impedance of thecoating together with the smooth character thereof are such that therate of longitudinal movement of the metal mold is greatly accelerated.This action in itself minimizes the development of shills and theresultant laps or cold shuts in the centrifugal casing, which arefurther and cooperatively avoided by the proper amount of thermalimpedance imparted to the coating through the practice of thisinvention.

In order that the herein disclosed improvements may be better understoodreference is made to the accompanying drawings wherein are illustratedcertain presently preferred modifications of the invention, togetherwith certain presently preferred methods of practicing the same.

In the drawings:

FIGURE 1 is a side and end isometric view of apparatus employed incoating a centrifugal mold of relatively small diameter;

FIGURE 2 is a side and end isometric view of apparatus employed incoating a centrifugal mold of relatively large diameter;

FIGURE 3 is an isometric view partially cut away of a centrifugal moldcoated in accordance with the invention;

FIGURE 4 is a cross-sectional view of the coated mold illustrated inFIGURE 3;

FIGURE 5 is an isometric view of a complete coating machine and line forpracticing the invention; and

FIGURE 6 is a top plan view of the carriage of FIG- URE 5.

Referring now more partciularly to FIGURE 1 of the drawings, a methodand apparatus are illustrated therein for applying a smooth coating 10of substantially uniform thickness and high thermal impedance to theinner or molding surfaces of a centrifugal mold 12. An annularly orcircumferentially shouldered recess 13 is formed at each end of the mold12 to recess suitable stop members (not shown) inserted therein duringthe casting operation to limit the longitudinal flow of the molten metalcharge. The mold 12 in this arrangement is supported for horizontalrotation about its longitudinal axis upon spaced pairs of rollers 14.The rollers 14 are rotated all in the same rotational direction, by asuitable drive mechanism including motor 16. The pairs of rolls 14 arespaced in this example such that they engage the centrifugal mold 12adjacent the ends respectively thereof. Desirably, one pair of rolls 14can be moved longitudinally of the mold 12 relative to the other pair ofrolls 14, by conventional means (not shown), so that the centrifugalmolds of differing lengths can be accommodated.

For purposes of applying one of the aforementioned coating suspensionsto the inner surfaces of the mold 12, a suitable spray nozzle or head 20is mounted on the end of lance or supporting member 22. The lance 22 isslidably mounted upon a suitable support 24 therefor and is therebydisposed for longitudinal and axial movement of the lance 22 and thespray nozzle 20 throughout the length of the mold 12. In furtherance ofthis purpose, the lance can be provided with a rack thereon 26 of alength equivalent to that of the mold 12, or to that of the longest moldanticipated for use with the apparatus,, and disposed therealong forcooperatoin with pinion 28 driven by a suitable motor and gear reductionunit indicated generally by reference character 30. Desirably, theoutput speed of the drive unit 30 is variable such that the pinion 28 inengagement with the lance rack 26 operates to drive the lance at a speedin the neighborhood of about 27 feet per minute along the longitudinalaxis of the tube 12.

In this arrangement of the invention, as seen in FIG- URE 1, the spraynozzle 20 is of the ring-type and emits a circumferential or ring sprayfrom a circumferential slot, which is substantially perpendicular to themold axis and to the mold surfaces thereof. The spray nozzle 20preferably is aligned with the centrifugal mold axis and is insertedsubstantially concentrically of the mold 12 as the nozzle 20 is movedtherethrough by the lance 22 in order to deposit the coating suspensionequally and uniformly upon the adjacent mold surfaces.

To further aid in a uniform build-up of the coating and to preventcoating runs and roughness, the mold 12 is rotated about itslongitudinal axis, during the spraying operation, at a rotational speedof about 800 r.p.m. This rotational speed has been found to be fairlycritical, as speeds substantially above or below the aforementionedspeed tend to produce a roughened surface coating which is undesirablefor the reasons mentioned previously.

The coating suspension being used is supplied to the spray nozzle 20from a suitable container (not shown) and compressed air for controllingthe atomization thereof are supplied to the spray nozzle 20 throughsuitable conduits represented by the hose connections 34 and 36respectively.

As noted previously, in order to obtain an exceptionally smooth coating,the spray noozle 20 is supported as close to the mold surface aspractical during the spraying operation at a maximum distance of about4%. inches. Inasmuch as the spray nozzle 20 is supported concentricallyof the centrifugal mold, in the arrangement of the apparatus accordingto FIGURE 1, the diameter of the mold becomes a limiting factor in theuse of this arrangement of the apparatus. When the mold diameter isincreased to an extent such that the radial distance between the moldsurface being coated and the spray nozzle 20 displaces the spray nozzleat too great a distance from the surface being coated for the requisitecoating smoothness, the spraying apparatus as arranged in accordancewith FIGURE 2 of the drawings is preferably utilized. In the latterarrangement of the invention, as illustrated in FIG- URE 2, thering-type spray nozzle 20 of FIGURE 1 is replaced by a fan spray nozzle38 having coating and compressed air connections denoted at 40 and 42.The spray nozzle 38 is similarly mounted on the adjacent end of lance22' for reciprocable and axial movement thereof relative to thecentrifugal mold 12, and is supported at a maximum spray distance ofabout 4 /2 inches.

In this example, however, the spray nozzle 38, is of the fan type and issupported perpendicularly to the centrifugal mold axis and thus to themold surfaces to which the coating 10' is being applied. The axis of thefan or sheet of the coating spray 44 is, therefore, likewise directednormally of the coated surfaces 10'. The lance 22' is not necessarilypositioned coaxially of the centrifugal mold 12' when reciprocatedtherethrough but rather can be supported, in this example, at suchelevation parallel to the axis as determined by the optimum spraydistance between the spray nozzle 38 and the mold surfaces. Infurtherance of this purpose, the lance 22 is secured in a guide member46, which in turn is slidably mounted upon the vertical lance support24. The guide member 46 is provided with screw adjusting means 48whereby the clamping member can be secured at a selected elevation alongthe upright lance support 24.

In the latter arrangement of the invention, the interior of the mold 12'can be coated by moving the lance 22' at a longitudinal rate relative tothe mold 12 of about 27 feet per minute, which is sufficient to coat theinterior of the mold 12' in one pass on small diameter rolls, howeverlarge diameter molds may require up to 6 or 7 passes. At the same time,the mold 12 is rotated at a rotational speed of about 500 r.p.m. in theexample of FIGURE 2, which depicts a mold of about 17 inches indiameter.

The rotational speed of the mold 12 or 12' during the coating operationis somewhat critical as noted previously and is related to the diameterof the mold surface. In the arrangement of FIGURE 1, for example, a mold12 having a diameter of about 6 inches was utilized and was rotated at aspeed of about 800 r.p.m. On the other hand, in the centrifugal moldcoating operation -as described in FIGURE 2 a centrifugal mold 12 havinga diameter of 17 inches was rotated at a speed of 500 r.p.m. Other moldsizes will dictate rotational speeds relative to the aforementionedspeeds depending upon their diametric relationship.

As illustrated in FIGURE 3, the coated surfaces produced with theapplication of FIGURE 1 or 2 affords a very smooth mold lining, whichcan be further finished as by sanding or grinding, for example, throughthe use of suitable tool (not shown) affixed to the forward end of thelance 22 in place of the spray nozzle 20 or 38. As better 9 shown inFIGURE 3, the resulting surface of a centrifugal casing made inaccordance with the invention presents a very smooth surfacecharacteristic, regardless of the size or outside diameter of thecentrifugal casting. Thus a superior degree of smoothness can beobtained and the usual, rough surfaces of the prior art are obviated.

In FIGURE there is illustrated a complete assembly for coating rotarymolds. In such an assembly a series of molds 12 are mounted side by sideon roll carriers as shown in FIGURE 1. Spaced nails 50, 50a and 51 passin front of such molds and perpendicular to their axis. A movable bridge52 is mounted on wheels 53 which run on rails 50, 50a and 51. A carriage54 is mounted on Wheels 55 to run on rails 56, 57 on bridge 52. Therails 56 and 57 are perpendicular to rails 50, 50a and 51. The carriage54 carries a tank 58 of coating agent together with lance support frame59 and drive motor 60 for driving wheels 55. A lance 61 of the sameconfiguration as lance 22 of FIGURE 1 is mounted in frame 59, and ismovable in guide frame 62 on trunnions 63. The guide frame 62 isvertically movable in vertical frame 64 on the end of bridge 52 oppositethe carriage. The treating fluid or coating is delivered to pipes 65 and66 and to a spray head 67 identical with pipes 34 and 36 and spray head20 of FIG- URE 1. The spray head is advanced into and withdrawn from themolds by moving carriage 54 on tracks 56 and 57.

From the foregoing it will be apparent that novel and efiicientcentrifugal casting techniques have been disclosed herein. While certainpresently preferred embodiments of the invention, together with certainpresently preferred methods of practicing the same have been shown anddescribed herein, it is to be distinctly understood that the inventionis not limited thereto but may be otherwise variously embodied andpracticed within the scope of the following claims.

I claim:

1. A centrifugal casting mold comprising an elongated tubular non-ventedmetal member, an annular stop member receiving recess in each end ofsaid tubular member, means for rotating said tubular member about itslongitudinal axis, and a smooth refractory nonhydrocarbon coatingadhered to the metal mold surfaces of said centrifugal mold andextending substantially between said recesses, the thickness of saidcoating providing a thermal barrier for the elimination of chills in thecharge of molten metal supplied to said centrifugal mold.

2. A centrifugal casting mold comprising an elongated tubular non-ventedmetal member, an annular stop member receiving recess in each end ofsaid tubular member, means for rotating said tubular member about itslongitudinal axis, and a smooth refractory nonhydrocarbon 10 coatingadhered to the metal mold surfaces of said centrifugal mold andextending substantially between said recesses, the thickness of saidcoating providing a thermal barrier for the elimination of chills in thecharge of molten metal supplied to said centrifugal mold, the thick nessof said coating varying between 5 and 125 mils.

3. A centrifugal casting mold comprising an elongated tubular nonventedmetal member, an annular stop member receiving recess in each end ofsaid tubular member, means for rotating said tubular member about itslongitudinal axis, and a smooth refractory nonhydrocarbon coatingadhered to the metal mold surfaces of said centrifugal mold andextending substantially between said recesses, the thickness of saidcoating providing a thermal barrier for the elimination of chills in thecharge of molten poured into said centrifugal mold, the thickness ofsaid coating varying between 5 and mils for centrifugal molds of about 9inches in diameter or less and between 80 and mils for centrifugal moldsgreater than about 9 inches in diameter.

4. The combination according to claim 1 characterized in that saidcoating is refractory based, such as zirconium oxide based.

5. The combination according to claim 4 characterized further in thatsaid refractory coating includes a suspending agent such as bentoniteand a thermal impedance and stripping agent such as diatomaceous earth.

6. The combination according to claim 4 characterized further in thatsaid refractory coating includes a binder selected from at least one ofthe group consisting of bentonite, and sodium silicate.

7. The combination according to claim 4 characterized further in thatsaid refractory coating includes a binder selected from at least one ofthe group consisting of bentonite and sodium silicate; a thermalimpedance and stripping agent such as diatomaceous earth, and asuspending agent selected from at least one of the group consisting ofbentonite and sodium silicate.

References Cited UNITED STATES PATENTS 2,874,412 2/1959 Flemming et al.164-298 X 2,030,105 2/1936 Eurich et al. 164-286 2,731,690 1/1956Coupland et al 164-33 2,749,587 6/1956 Richards et al 164-33 3,211,56010/1965 Fair 164-33 I. SPENCER OVERHOLSER Primary Examiner. ROBERT D.BALDWIN, Assistant Examiner.

US. Cl. X.R. 164-33

